The overall aim of this project is to understand the role of nontrivial systematic errors in the overall accuracy of multileaf collimator (MLC) -based megavoltage (MV) photon-beam intensity modulated radiation therapy (IMRI-) delivery and dose calculation. According to our preliminary data, nontrivial systematic errors in IMRT delivery and plan calculation exist with significant frequency and have the potential to conspire to be clinically significant. A complete experimental characterization of static and dynamic MLC-based IMRT delivery is proposed. This experimental characterization includes the accurate simultaneous measurement of the dose distributions produced by IMRT using a novel radiochromic film dose-imaging system, and the delivered field shapes and fluences using a high-speed scintillation camera system. Results from this work will provide a ranking of the importance of the different sources of error for the development of strategies to minimize IMRT delivery errors. The data from this characterization will allow mechanical misalignment and dose delivery errors to be compensated for by incorporating the feedback of these measured parameters into a treatment-planning algorithm. From this vantage, the accuracy of the IMRT dose calculational algorithms will be assessed. Results from this work will provide a paradigm for closing the loop between the clinical treatment planning system and the MLC IMRT delivery system.